Maybe,
\(\cfrac{q^2}{4\pi \varepsilon_o r^2}=\cfrac{q}{4\pi \sqrt{\varepsilon_o} r^2}.\cfrac{q}{\sqrt{\varepsilon_o}}\)
that, the change in \(KE\) per unit test charge is,
\(\cfrac{q}{4\pi \sqrt{\varepsilon_o} r^2}\)
This would change the definition of \(\varepsilon_o\) in this model, and the symbol \(\sqrt{\varepsilon}\) replaces \(\varepsilon_o\). The correction factor to \(c\) considering \(\sqrt{\varepsilon}\) remains,
\(\cfrac {2ln(cosh(\theta_{\psi})) }{ \mu _{ o } }\)
the same.
